C＃-将数据加载到SQL Server中并合并（如果已存在）

Question

Suppose I have the following table in SQL Server:

MyTable:
IDCol:     Val1:    Val2:
1          a        b
2          c        d
...

And, I am only able to access / modify it via direct SQL statements (meaning I can't put a file in a location and tell it to upload that file, for example)

So, currently, in my C# code, if I want to insert values into this table, I'm actually writing SQL such as:

INSERT INTO MyTable (IDCol, Col1, Col2) Values (.....)

But now I have to take into account the possibility of a value already existing in the table and, if it does, to update that row.

I know I can do this via a Merge , but how could I do it via direct SQL statements?

1. Do I create a temporary table, do the merge, then delete it?
2. Do I query the rows that already match, update them, then do an insert on the remaining?
3. Is there some kind of other SQL syntax for doing such a thing otherwise?

And, if #1 is the correct way to go, how can I do this such that, if I have 2 instances of my program running, I'm not double-creating a temporary table by the same name?

Answer 1

You can use the merge command as you proposed or use an if exists like this:

IF EXISTS(SELECT * FROM myTable WHERE Id = @id)
UPDATE myTable SET x = @x WHERE Id = @id
ELSE
INSERT INTO myTable (Id, x) VALUES (@id, @x)

Answer 2

Assuming you are doing merge based on ID column, and assuming you are firing insert row by row, so you have three variables @idcol, @col1, @col2 , then use the below query

--DECLARE @IDCol int
--DECLARE @Col1 varchar(10), @Col2 varchar(10)
--SET @IDcol=2
--SET @Col1='A'
--SET @col2='C'

IF NOT EXISTS( SELECT 1 FROM MyTable WHERE IDCol=@IDCol)
BEGIN
INSERT INTO MyTable (IDCol, Col1, Col2) Values (@IDcol,@col1,@col2)
END
ELSE
BEGIN
UPDATE MyTable
SET Col1= @Col1, Col2=@Col2
WHERE IDCol=@IDCol
END

--SELECT * from MyTable

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